>> reporter: president obama held his final ohio event in columbus. an estimated 15,000 supporters and a pitch aimed at ohio. >> i'm proud we saved the auto industry. but i'm even prouder that we're making better cars now. >> the president visited volunteers and called in ohio voter. >> this is barack obama. and i hope that we bring it home tomorrow. >> reporter: for days republican volunteers like jeremy bosco have worked the cincinnati/hamilton county, ohio suburbs to be sure romney backers vote. >> we'll be there tuesday morning. >> thank you so much. >> reporter: jeremy knows ohio must win for romney. do you ever figure jeez, if i do a great job now, in this county, i could get my guy to the white house, you? >> in a small way, yes. >> reporter: ohio's early voting has been busy, but republican poll watchers could challenge the balance of thousands of these and tomorrow's voters. >> if you have a very tight race in the state of ohio, you could very well have a decision that we won't know the results of for two weeks. >> reporter: would no time to